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UBL seems off

Posted by ttabbal 
UBL seems off
June 18, 2020 06:59PM
I'm trying to get UBL working with a BLTouch probe. I have the probe working, and homing works. I can also run the UBL mesh probe and get what looks like reasonable results. However, when it's active, Z0 is actually more like Z-4. I could edit the mesh, and that might work, but it seems too consistent to be a bug and more likely something I'm doing wrong. I have attached the config files and logs of some testing. I determined the Z nozzle/probe offset by homing, then moving down till paper drags on the nozzle. Then using M114 to adjust the offest. The offset consistently gives good Z0 with leveling disabled after a G28. M502/M500 before every test.

Hardware is an older Lulzbot mini v1, mini Rambo board, with the bltouch wired per this post. [reprap.org]

I tried the 2.0.x and bugfix-2.0.x branches, they had similar results.
open | download - ttabbal-config.zip (70.2 KB)
Re: UBL seems off
July 02, 2020 06:05PM
Did you generate your mesh (G29 P1) before or after setting the probe offset? You should always run the G29 P1 after setting the correct probe offset to ensure that it has the correct "0". I can't tell from your logs whether the mesh was generated before or after the probe offset was set.

Also, make sure that the output of M851 matches what you have set in NOZZLE_TO_PROBE_OFFSET.
Re: UBL seems off
July 02, 2020 06:17PM
Thanks for getting back to me. I set the offset in the code and did a reset (M502) to ensure it was in M851.

I think I got it sorted out. I was off with the Z offset when setting it with the leveling system disabled. I adjusted it with leveling on and was able to get a probe to run with "G29 P1" then have a correct height later. I've managed to get some decent prints since, so I think I'm good now.
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